1. Field of the Invention
The present invention relates to an image forming apparatus employing an electrophotographic method such as a copier, a printer, a facsimile, or a multifunction product and a belt device installed therein, and more particularly, to a belt device and image forming apparatus that corrects meandering of a belt member such as an intermediate transfer belt, a transfer belt, or a photosensitive belt.
2. Description of the Related Art
A tandem-type color image forming apparatus including an intermediate transfer belt (belt device) is a typical type of an image forming apparatus such as a copier and a printer (see, for example, Japanese Patent Application Laid-open No. 2006-343629 and Japanese Patent Application Laid-open No. 2001-83840). Four photosensitive drums (image carriers) are provided side by side facing an intermediate transfer belt (belt member). The four photosensitive drums then form toner images for black, yellow, magenta, and cyan, respectively. The toner images for each of the colors formed on each photosensitive drum are then transferred and superimposed on the intermediate transfer belt. The toner images formed on the intermediate transfer belt are then transferred onto a recording medium as a full color image.
Technology such as disclosed, for example, in Japanese Patent Application Laid-open No. 2006-343629 and Japanese Patent No. 3082452, is also well-known. Here, at an image forming apparatus, displacement of an intermediate transfer belt in a width direction is detected and meandering (variation in a width-wise direction) of the intermediate transfer belt is corrected based on results of the detection. Specifically, in Japanese Patent Application Laid-open No. 2006-343629, an extent of displacement of a contact that abuts with an end in a width direction of the intermediate transfer belt (endless belt) and reciprocates in accordance with displacement of the intermediate transfer belt is detected by a displacement sensor. Displacement (meandering) of the intermediate transfer belt is then corrected by a meandering correction roller based on the detection results of the displacement sensor. Tilting of a rotational axis of a meandering correction roller is then changed so as to correct meandering of the intermediate transfer belt by causing a coupling member (reciprocating arm) coupled to the meandering correction roller where the intermediate transfer belt is suspended in a tensioned state to be reciprocated by an operation of an eccentric cam.
On the other hand, technology is disclosed in Japanese Patent No. 3082452 where a belt device includes a transfer belt (transfer material conveyor belt). Tilting of a rotational axis of a tensioning roller is then varied in order to correct meandering of the transfer belt by reciprocating a coupling member (support arm) coupled to the tensioning roller that tensions the transfer belt using a cam action.
There are also cases with image forming apparatus such as the image forming apparatus of Japanese Patent Application Laid-open No. 2006-343629 where the reciprocating arm coupled to the meandering correction roller is pinched by the coupling member and therefore does not follow the action of the eccentric cam. In this event, the reciprocating arm can stop in a raised state even if urged by a spring. Tilting of the rotational axis of the meandering correction roller cannot then be changed and it is no longer possible to correct meandering of the intermediate transfer belt.
Such problems are not limited to belt devices using an intermediate transfer belt as a belt member, but are common to belt devices that correct meandering of belt members such as a belt device using a transfer belt as a belt member or a belt device using a photosensitive belt as a belt member. It is therefore possible to provide a belt device and image forming apparatus capable of accurately correcting meandering of a belt member without inappropriate reciprocation of a coupling member using a comparatively straightforward structure even when a coupling member coupled to a roller member that corrects meandering of a belt member is pinched.